For example, as touch panels that are provided on two surfaces of a monitor, a touch panel-equipped information terminal device exists that is provided with: a first touch panel that is superimposed on a monitor and is used to select objects on a monitor screen that are to be operated; and a second touch panel that is provided on a rear side of the monitor and is used to move, enlarge, or reduce the selected objects. This touch panel-equipped information terminal device integrates the operations of the first and second touch panels and displays them on a single monitor screen (see, for example, Patent document 1).
Moreover, an information display device also exists that is provided with a pair of touch panels that are each placed on a different surface of a main body of the device, and that controls displays in accordance with a combination of inputs that are made into the pair of touch panels (see, for example, Patent document 2).
Furthermore, a terminal device also exists that, in order to optimize the user interface to correspond to the manner in which it is being held, detects the manner in which the terminal device is being held using two operating units that are provided on top of a display unit and on the rear surface of the display unit, and alters the user interface or alters the association with the entire display surface of the operating unit on the rear surface in accordance with manner in which the terminal device is being held so that it is suitable for the left hand or the right hand that is holding it (see, for example, Patent document 3).